Motor control



Jan. 11, 1938. c, PEARCE 2,105,005

MOTOR CONTROL Original Filed Oct. 12, 1952 2 sheetsrsheet 1 Jan. 11,1938. c PEARCE 2,105,005

MOTOR CONTROL Original Filed Oct. 12, 1932 2 sheets sheet 2 Cswvsmora.

' BY w fl ATTORNEYS Patented Jan. 11, 1938 PATENT OFFICE MOTOR CONTROLGeorge C. Pearce, Dayton, Ohio, assignor, hy

mesne assignments, to General Motors Oomration, Dayton, Ohio, acorporation of Dela- Original application October 12, 1932, Serial No.639,461. Patent No. 2,018,898, dated October Divided and thisapplication May 20, 1985, Serial No. 22,422

18 Claims.

This application is a division of my copending application Serial No.639,461, filed October 12, 1932, now Patent No. 2,018,896, dated October29, 1935.

This invention relates to refrigeration and/or to starting controls forelectric motors.

Certain types of refrigerating systems operate intermittently, thetemperatures are maintained in the object to be cooled by starting andstopping the refrigerating system to produce refrigorationintermittently. Other types of refrigeration systems operatesubstantially continuously and some type of throttling or governingdevice is provided for varying the refrigerating capacity of the systemin accordance with refrigeration demands in such a manner that thedesired temperatures are maintained in the object to be cooled. Ineither case, the refrigerating system is stopped periodically foradjustments, defrosting, or for transportation of the system. Thesystem, if it be of the compressor-condenserevaporator type, isgenerally driven by an electric motor and it is necessary to provide acontrol for the electric current to the motor so that it may startproperly and unfailingly. It is among the objects of this invention toprovide a starting control for an electric motor which is capable ofgoverning the current flowing to the motor efllciently and withoutlikelihood of failure, regardless of unfavorable operating conditionsand varying line voltages. Further objects and advantages of the presentinvention will be apparent from the following description, referencebeing had to the accompanying drawings, wherein a preferred form of thepresent invention is clearly shown.

In the drawings:

Fig. 1 is a diagrammatic showing of a refrigerating system embodyingfeatures of this invention;

Fig. 2 is a diagrammatic showing of a slightly modified form of theinvention.

A refrigerating system embodying features of this invention may includea compressor III delivering refrigerant to a condenser II from whencethe refrigerant flows to the evaporator I2 and returns through thereturn line It to the compressor I 6. Between the condenser II and theevaporator I2 is an expansion device I l which maintains the necessarypressure differential between the condenser II and the evaporator I2.Preferably this refrigerating system is of the substantiallycontinuously operating type in which the parts are so co-related withthe refrigeration demands of the object to be cooled that the systerninherently maintains the desired temperature in the objectnotwithstanding variations in the atmospheric temperature. Such a systemincludes a continuously open expansion device in the form of a fixedelongated orifice. If the system should be stopped for any reason, thepressures within the refrigerating system equalize within a relativelyshort time such as within one quarter to one half hour. Such a system ismore particularly described in the application of Andrew A. Kucher,Serial No. 599,239 flied March 16, 1932 to which reference is herebymade for further disclosure of such a system.

The compressor I is driven by an electric motor I5 which may be placedin a hermetic casing Illa with the compressor, and which may be of thesplit phase type having a rotor Ila, a running winding I6 and a startingwinding I1. My improved control so governs the flow of current to thesewindings, that the current flows to both windings during the necessarynormal starting period of the motor and the current is disconnected fromthe starting winding I! after the termination of the normal startingperiod of the motor. To this end, as shown in Fig. 1, a common lead lineIt is connected to the running and starting windings at I9. Another leadline 20 is divided into a starting lead line 2| connected to thestarting winding at 22 and also into a running lead line 23 connected tothe runnin8 winding It at the point 24. An electromagnet 25 is placed inthe running lead line 23 and is connected by the branches 26 and 21 inthe running lead line. A shunt is placed in the running lead line sothat the electromagnet 25 may be shunted out of the system, and thisshunt may include a timing device 28, conveniently in the form of abimetallic U-shaped member connected by the shunt branches 29 and 36 ofthe running lead line. The electromagnet 26 is provided with an armature3i which includes means or contacts 32 and 33 for opening and closingthe starting lead line 2i. The armature 3i can retract from the magnet25 a sufllcient distance 3|. such that it is attracted to the magnet 26in response to the starting surge current passing through the runningwinding IE, but the space is sumciently large that the armature II isnot attracted to the magnet during the normal running current flowingthrough the running winding 11', for anyreason, the armature ll ispermitted once to assume its retracted position.

In addition, an overload device 36 is placed in the electric circuit, sothat it stops the flow of current in response to an excess currentflowheated beyond a normal temperature by the resistance 31 causes thelever 33 to pivot about the point 39 and open the contacts 40 to stopthe flow of current to the motor i5.

The operation of the system shown in Fig. l is as follows: When currentis first caused to flow through the system, it passes through the leadline 20, the running lead line 23, the running winding i5, and thecommon lead line i5. At this time, the current flows through thebranches 25 and 21 and the electromagnet 25. The electromagnet, inresponse to the starting surge current through the running winding i6,attracts the armature 3i, so that it pivots about the fulcrum 4i andcloses the contacts 32 and 33, thus causing current to flow through thestarting lead line 2i and the starting winding ii. The starting currentin passing through the timing device 28, which, in this form, is abimetallic U-shaped member, causes it to bend to close contacts 42. Whenthese contacts are closed, the electromagnet is shunted out of thecircuit, the current flowing through the branches 29, 30, a portion ofthe member 28 and contacts 42. The time required for the completion ofthis bending action of the timing device 28 is suiliciently long, sothat the contacts 42 are not closed until after the normal period oftime required for the motor to start. After this period of time, themagnet 25 is shunted out of the circuit and the armature 3i retractsfrom the magnet 25 and opens the contacts 33 and 34, thus stopping theflow of current to the starting winding ii. Bimetallic member 28 is socalibrated, that when the starting current ceases to flow through it, itseparates the contacts 42 and thus the current flows to the motor onlythrough the lead line 20, the branches '26, 27, and the electromagnet25, the running Winding i 6, and the lead line i8. Since the motor hasattained speed, the current flowing through the electromagnet 25 is onlythe normal running current and this is insuflicient to attract thearmature 3i to the magnet 25 after the armature has been permitted toretract by the shunting action heretofore described. The motor continuesto operate in this manner until it is stopped either by the overloaddevice 35, by a thermostatic switch i2a or similar device which controlsthe refrigerating effect of the system, or by any other automatic ormanual switch which may be conveniently placed in the system.

In the modification shown in Fig. 2, the refrigerating system may beidentical with that shown in Fig. 1 and hence corresponding parts aregiven identical numbers. The motor i 5 may also be identical with thatshown in Fig. 1 and hence its rotor, running winding and startingwinding are given identical numbers. In this modification a common leadline [8 is also provided, this being connected to the running andstarting windings at the point i9. Another lead line 20 is providedhaving the overload device 35 identical with that described in Fig. 1including the bimetallic member 36 and the resistance 31, arm 38,fulcrum 39, and contacts 40. The starting line 2ia and the running leadline 23a are slightly modified.

The branch 50, timing device 52 and branch 51 are parts of both therunning lead line 23a and the starting lead line Zia. From the point 51aon part of the running lead line 23a includes the branch 55,electromasnet l5 and branch 55 leading to the running winding ii at 24.Another part 01' the running lead line includes the contacts 53 and thebranch 54. The starting lead line 2la includes the branch 50, contactsii, 52, and the branch 62 leading to the starting winding i1 and 22.

In modification shown in Fig. 2, when the current is first introducedinto the system, it flows through the lead 20, contacts 40, resistance31, branch 55,- legs 5i, 55, branches 51, 55, electromagnet 58, branch55, running winding I5, and common lead ii. The current flowing throughthe magnet 55 attracts the armature 54 pivoted at 55 and closes thecontacts 5i and 52. Current then also flows through these contacts andthe branches 60 and 53 to the starting winding ii. The current flowingthrough the timing device 52, which at this time includes the totalcurrent required by the starting and running windings under startingconditions is suflicient to cause the device 52 to close the contacts 53after the normal starting period of the motor, and the device 52 is socalibrated that it will not close these contacts until the motor hasstarted. When the contacts 53 are closed, the electromagnet 55 isshunted by a flow of current through the leg 5i contacts 53, branches 54and 55 to the running winding i6. When this shunting action occurs, thearmature 54 retracts from the magnet and opens the contacts 5i and 52,thus stopping the flow of current to the starting winding IT. Theresistance of the device 52 is so calibrated that the current flowing tothe running winding alone under any condition and passing through theleg 5i alone, or through both legs 5i and 53, is insufflcient tomaintain the device 52 in a sutiiciently heated condition and thereforethe contacts 53 begin to separate as soon as the starting winding is cutout. When the contacts 53 separate current flows from the line 20through the branch device 52, branches 5'! and 58, electromagnet 59 andbranch to the running winding without closing the contacts ii, 62, sincethe magnet 53 is so calibrated that it cannot attract the armature 64 toit even with the highest normal running current passing through it, butcan be attracted by the starting surge current flowing to the runningwinding. The device 52 is therefore cooled on and in readiness toinitiate a starting cycle practically as soon as the previous startingcycle is terminated.

In both modifications shown in Figs. 1 and 2, the cooling action of thetiming devices 28 and 52 are so calibrated with respect to the coolingaction 01' the overload device 35, that, should the overload device 35open the contacts 40, the timing devices 28 and 52 will have cooled andbe in readiness to function before the overload device 35 has cooled andreclosed contacts 40. This is accomplished by making the members of theproper relative weight or by proper thermal insulation of the members toaccomplish this result, as will be understood by those skilled in theart.

In the type of continuously operating system described in theapplication of Andrew A. Kucher, above referred to, it sometimes happensthat the source of electric current fails temporarily either because ofan electric storm or other causes, but is restored in a relatively shorttime. Sometimes the temporary failure is of suflicient length to permitthe refrigerating system to equalize as to refrigerant pressures, but atother times the failure is of such a short duration that the refrigerantpressure cannot equalize sufficiently to unload the compressor III topermit the motor IE to start. Under these conditions, when the currentreturns, the starting cycle will take place as usual, the currentflowing through both the running winding and starting windings for thenormal starting period; but since the motor is unable to start becauseof the high torque required, the current flowing through both windingsduring the starting period and the subsequent flow of current throughthe running winding of the stalled motor eventually causes the overloaddevice 35 to open the contacts 40. After encountered during normaloperation.

starts to cool, but requires a longer length of time than is required bythe timing devices 28 or 52 and hence when the overload device hascooled sufficiently to close the contacts 40, the timing devices 28 and52 are in readiness to reinitiate the starting cycle. Another startingcycle will then be completed, and if the compressor still prevents themotor from starting, another overloading action will occur and thus asmany starting cycles will be repeated as required until the refrigerantpressures have equalized sufiiciently to permit the motor to start.Since the system equalizes within 5 to 15 minutes, and since eachoverloading cycle requires from one to two minutes, the number of falsestarts is not excessive and will not burn out the motor.

While in the preferred embodiment, the timing devices 28 and 52 are socalibrated that they shunt the electromagnets every time that the motoris started, yet it is within the purview of this invention that thesetiming devices can be used merely as protective or safety devices forthe usual surge current starting relay heretofore commonly used. Thus inFig. 1, the electromagnet 25 may be so calibrated that it attracts thearmature 3| when the starting surge current flowing to the runningwinding passes through it, but releases the armature because of thedecrease in current when the motor has attained sufiicient speed sothatit can attain its normal running condition. This type of starting relaycan be calibrated for the lowest likely voltage to be Such a relay whenso calibrated, however, is likely to fall to function when unusuallyhigh voltages are encountered. When such voltages are encountered, thecurrent flowing to the running winding does not drop sufficiently afterthe motor has attained its starting speed to release the armature 3i andthus the starting winding is not cut out as long as the high voltagescontinue. The device 28, under these conditions of high voltage, can beused as a safety device and can be so cal ibrated that it starts to butdoes not close the contacts 42 under the normal or low voltagesheretofore described, but that it will close the contacts 42 after thetermination of the normal starting period and after failure of thearmature 3| to drop during high voltages. I'hus under such use of myinvention, the timing device 28, while it still does shunt theelectromagnet occasionally after the starting period, is used merely asa safety device which closes the contacts 42 only when the voltages arehigh enough to prevent the armature 3i from functioning normally.

Likewise the device 52 of Fig. 2 can be used merely as a safety deviceto operate only under the high voltages just described with respect toFig. 1. In this case the electromagnet 59 can be so calibrated that forlow or normal voltages it attracts the armature 64 by the running surgecurrent during the starting period of the motor, but releases thearmature when the running winding current drops after the motor hasattained its starting speed. When high voltages are encountered, andthearmature B4 fails to drop, the device 52 responds as a safety deviceand closes the contacts 53 to shunt the magnet 59 and permit thearmature 64 to drop and thus cut out the starting winding IT. Theelectromagnet is then unable to reclose the starting contacts even undersuch high voltages. It is to be understood that such use of the timingdevices 28 and 52 merely as safety devices as above described comeswithin the purview of my invention.

While the form of embodiment of the invention as herein disclosed,constitutes a preferred form, it is to be understood that other formsmight be adopted, all coming within the scope of the claimswhich follow.

What is claimed is as follows:

1. In combination, a motor having a starting winding and a runningwinding, a running lead line connected to said running winding, astarting lead line connected to said starting winding, an electromagnetin said running lead line, said magnet having an armature with means forclosing said starting lead line when said armature is attracted to saidmagnet and for opening said starting lead line when said armature isretracted from said magnet, a shunt in said running lead line aroundsaid electromagnet, and a timing device operable following the closingof the starting lead line circuit and responsive to flow of currentthrough said motor for closing said shunt after a period oi timefollowing the closing of said starting lead line.

2. In combination, a motor having a starting winding and a runningwinding, a running lead line connected to said running winding, astarting lead line connected to said starting winding, an electromagnetin said running lead line, said magnet having an armature with means forclosing said starting lead line when said armature is attracted to saidmagnet and for opening said starting lead line when said armature isretracted from said magnet, a shunt in said running lead around saidelectromagnet, and a timing circuit closing device operable mechanicallyindependently of said armature and responsive to flow of current throughsaid motor for closing said shunt after a period of time equal to thenormal starting period of said motor.

3. In combination, a motor having a starting winding and a runningwinding, a running lead line connected to said running winding, astarting lead line connected to said starting winding, an electromagnetin said running lead line, said magnet having an armature with means forclosing said starting lead line when said armature is attracted to saidmagnet and for opening said starting lead line when said armature isretracted from said magnet, a shunt in said running lead line aroundsaid electromagnet, and a thermostatic device responsive to flow ofcurrent through said motor for closing said shunt after a period of timeequal to the normal starting period of said motor.

4. In combination, a motor having a starting winding and a runningwinding, a running lead line connected to said running winding, astarting lead line connected to said starting winding, an electromagnetin said running lead line, said magnet having an armature with means forclosing said starting lead line when said armature is attracted to saidmagnet and for opening said starting lead line when said armature isretracted from said magnet, a shunt in said running lead line aroundsaid electromagnet, and a thermostatic device operable mechanicallyindependently of said armature and responsive to flow of current throughsaid motor for closing said shunt after a period of time equal to thenormal starting period of said motor.

5. In combination, a motor having a starting winding and a runningwinding, an electromagnet in series with said running winding, anarmature for said magnet closing a circuit to said starting winding inresponse to the starting surge current passing through said magnet tosaid running winding and a current responsive device in said circuitoperable mechanically independently of said armature shunting saidelectromagnet after the normal period of time required for said motor tostart.

6. In combination, a motor having a starting winding and a runningwinding, a running lead line connected to said running winding, astarting lead line connected to said starting winding, an electromagnetin said running lead line, said magnet having an armature with means forclosing said starting lead line when said armature is attracted to saidmagnet and for opening said starting lead line when said armature isretracted from said magnet, a shunt in said running lead line aroundsaid electromagnet, and a safety timing device operable mechanicallyindependently of the armature and responsive to the flow of currentthrough said motor for closing said shunt.

'7. In combination, a motor having a starting winding and a runningwinding, a running lead line connected to said running winding, astarting lead line connected to said starting winding, an electromagnetin said running lead line, said magnet having an armature with means forclosing said starting lead line when said armature is attracted to saidmagnet and for opening said starting lead line when said armature isretracted from said magnet, a shunt in said running lead line aroundsaid electromagnet, and a safety timing device operable after theclosing of said starting lead line and responsive to the flow of currentthrough said motor for closing said shunt.

8. In combination, a motor having a starting winding and a runningwinding, an electromagnet in series with said running winding, anarmature for said magnet closing a circuit to said starting winding inresponse to the starting surge current passing through said magnet tosaid running winding and a self resetting current responsive deviceoperable after the closing of said starting winding circuit for shuntingsaid electromagnet after the normal period of time required for saidmotor to start and for opening said shunt after said armature has openedsaid circuit.

9. In combination, an electric motor having a starting circuit and arunning circuit, means energized by electric energy flowing through saidrunning circuit for connecting said starting circuit to a source ofelectric energy, and self resetting means operable after the connectingof said starting circuit to the source of electric energy and upon apredetermined condition in a motor circuit for shunting said firstmentioned means.

10. In combination, an electric motor having a starting circuit and arunning circuit, means energized by electric energy flowing through saidrunning circuit for connecting said starting circuit to a source ofelectric energy, and self resetting means operable mechanicallyindependently of said first mentioned means and upon a. predeterminedcondition in a motor circuit for deenergizing said first mentionedmeans.

11. In combination, an electric motor having a starting circuit and arunning circuit, means energized by electric energy flowing through saidrunning circuit for connecting said starting circuit to a source ofelectric energy, and self resetting means operable after the connectingof said starting circuit and upon a predetermined cumulative flow ofelectric energy through a motor circuit for deenerglzing said firstmentioned means.

12. In combination, an electric motor having a starting circuit and arunning circuit, means energized by electric energy flowing through saidrunning circuit for connecting said starting circuit to a source ofelectric energy, and self resetting circuit opening and closing meansoperable after the connecting of the starting circuit for deenergizingsaid first mentioned means after the motor has been properly energized.

13. In combination, a motor having a starting winding and a runningwinding, an electromagnet in series with said running winding, anarmature for said magnet closing the circuit to said starting winding inresponse to the starting surge current passing through said magnet tosaid running winding, and a self resetting current responsive -deviceoperable mechanically independently of said armature for shunting saidelectromagnet after the normal period of time required for said motor tostart and for opening said shunt after said armature has opened saidcircuit.

14. In combination, an electric motor having a starting circuit and arunning circuit, means energized by electric energy flowing through saidrunning circuit for connecting said starting circuit to a source ofelectric energy, and self resetting circuit opening and closing meansoperable mechanically independently of said first mentioned means fordeenergizing said flrst mentioned means after said motor has beenproperly energized and has started to rotate.

15. In combination, an electric motor having a starting circuit and arunning circuit, means energized by electric energy flowing through saidrunning circuit for connecting said starting circuit to a source ofelectric energy, and self resetting means responsive to cumulativeheating effect of the flow of energy through said motor for deenergizingsaid first mentioned means after the motor has been properly energized.

16. In combination, an electric motor having a starting circuit and arunning circuit, means energized by electric energy flowing through saidrunning circuit for connecting said starting circuit to a source ofelectric energy, a. shunt having a negligible amount of resistance forshunting said first mentioned means, said shunt being provided with anautomatically initiated self resetting circuit opening and closingmeans, said circuit opening and closing means being operated after theconnecting of said starting winding circuit upon a predeterminedcondition in a motor circuit for closing said shunt to completelydeenergize said first named means, said circuit opening and closingmeans being opened responsive to a. different predetermined condition ina motor circuit.

1'7. In combination, a motor having a starting winding and a runningwinding, an electromagnet in series with said running winding, anarmature for said magnet closing the circuit to said starting winding inresponse to the initial surge current passing through said magnet tosaid running winding, and self resetting means responsive to iii windingin response to the initial surge current passing through said magnet tosaid running winding, and a current responsive device in series with oneof said windings operable after the closing of the circuit to thestarting winding for shunting said electromagnet after the normal periodof time required for the motor to start.

GEORGE C. PEARCE.

